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  <title>React入门学习--状态提升 | 山岚 - 90码农历险记</title>
  <meta name="description" content="什么是状态提升？官网是这样解释的：  通常，多个组件需要反映相同的变化数据，这时我们建议将共享状态提升到最近的共同父组件中去。  我对“状态提升”的理解是，子组件A和子组件B需要进行数据交换/共享，则需要把他们俩需要交换数据的变量temp，放在他们最近的共同父组件内创建。这样，这两个子组件都可以访问到temp变量，并且还可以对temp变量进行修改。 说人话，“状态提升”可以帮你解决不同组件之间的赋">
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<meta property="og:description" content="什么是状态提升？官网是这样解释的：  通常，多个组件需要反映相同的变化数据，这时我们建议将共享状态提升到最近的共同父组件中去。  我对“状态提升”的理解是，子组件A和子组件B需要进行数据交换/共享，则需要把他们俩需要交换数据的变量temp，放在他们最近的共同父组件内创建。这样，这两个子组件都可以访问到temp变量，并且还可以对temp变量进行修改。 说人话，“状态提升”可以帮你解决不同组件之间的赋">
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<meta name="twitter:description" content="什么是状态提升？官网是这样解释的：  通常，多个组件需要反映相同的变化数据，这时我们建议将共享状态提升到最近的共同父组件中去。  我对“状态提升”的理解是，子组件A和子组件B需要进行数据交换/共享，则需要把他们俩需要交换数据的变量temp，放在他们最近的共同父组件内创建。这样，这两个子组件都可以访问到temp变量，并且还可以对temp变量进行修改。 说人话，“状态提升”可以帮你解决不同组件之间的赋">
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      <ol class="toc"><li class="toc-item toc-level-1"><a class="toc-link" href="#什么是状态提升？"><span class="toc-number">1.</span> <span class="toc-text">什么是状态提升？</span></a></li><li class="toc-item toc-level-1"><a class="toc-link" href="#详细代码执行流程"><span class="toc-number">2.</span> <span class="toc-text">详细代码执行流程</span></a><ol class="toc-child"><li class="toc-item toc-level-2"><a class="toc-link" href="#1-首先React先挂载Calculator组件。而Calculator组件会调用render-渲染页面UI"><span class="toc-number">2.1.</span> <span class="toc-text">1.首先React先挂载Calculator组件。而Calculator组件会调用render()渲染页面UI</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#2-Calculator组件的render-内定义一些变量接收数据。其中用到了三元表达式来调用温度单位换算或者赋值"><span class="toc-number">2.2.</span> <span class="toc-text">2. Calculator组件的render()内定义一些变量接收数据。其中用到了三元表达式来调用温度单位换算或者赋值</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#3-在Calculator组件的render-内的return-有三个组件。"><span class="toc-number">2.3.</span> <span class="toc-text">3.在Calculator组件的render()内的return()有三个组件。</span></a><ol class="toc-child"><li class="toc-item toc-level-3"><a class="toc-link" href="#A-两个输入框组件：TemperatureInput"><span class="toc-number">2.3.1.</span> <span class="toc-text">A. 两个输入框组件：TemperatureInput</span></a><ol class="toc-child"><li class="toc-item toc-level-4"><a class="toc-link" href="#1-TemperatureInput输入框组件需要接收3个参数：scale温度符号、temperature温度数值、onTemperatureChange调用哪个温度单位转换函数"><span class="toc-number">2.3.1.1.</span> <span class="toc-text">1. TemperatureInput输入框组件需要接收3个参数：scale温度符号、temperature温度数值、onTemperatureChange调用哪个温度单位转换函数</span></a></li><li class="toc-item toc-level-4"><a class="toc-link" href="#2-在render-内接受父组件Calculator的值，例如温度temperature，以及onChange事件执行函数"><span class="toc-number">2.3.1.2.</span> <span class="toc-text">2. 在render()内接受父组件Calculator的值，例如温度temperature，以及onChange事件执行函数</span></a></li><li class="toc-item toc-level-4"><a class="toc-link" href="#3-该组件的render-会渲染出一个输入框"><span class="toc-number">2.3.1.3.</span> <span class="toc-text">3. 该组件的render()会渲染出一个输入框</span></a></li><li class="toc-item toc-level-4"><a class="toc-link" href="#4-上面的input框有一个onChange事件，调用了handleChange-方法，代码如下："><span class="toc-number">2.3.1.4.</span> <span class="toc-text">4. 上面的input框有一个onChange事件，调用了handleChange()方法，代码如下：</span></a></li></ol></li><li class="toc-item toc-level-3"><a class="toc-link" href="#B-一个提供沸腾信息显示的BoilingVerdict，判断celsius是否大于等于100"><span class="toc-number">2.3.2.</span> <span class="toc-text">B. 一个提供沸腾信息显示的BoilingVerdict，判断celsius是否大于等于100</span></a></li></ol></li></ol></li><li class="toc-item toc-level-1"><a class="toc-link" href="#总结"><span class="toc-number">3.</span> <span class="toc-text">总结</span></a></li><li class="toc-item toc-level-1"><a class="toc-link" href="#完整代码"><span class="toc-number">4.</span> <span class="toc-text">完整代码</span></a></li><li class="toc-item toc-level-1"><a class="toc-link" href="#效果图"><span class="toc-number">5.</span> <span class="toc-text">效果图</span></a></li></ol>
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        <h1 id="什么是状态提升？"><a href="#什么是状态提升？" class="headerlink" title="什么是状态提升？"></a>什么是状态提升？</h1><p>官网是这样解释的：</p>
<blockquote>
<p>通常，多个组件需要反映相同的变化数据，这时我们建议将共享状态提升到最近的共同父组件中去。</p>
</blockquote>
<p>我对“状态提升”的理解是，子组件A和子组件B需要进行<strong>数据交换/共享</strong>，则需要把他们俩需要交换数据的变量temp，放在他们最近的共同父组件内创建。这样，这两个子组件都可以访问到temp变量，并且还可以对temp变量进行修改。</p>
<p><strong>说人话，“状态提升”可以帮你解决不同组件之间的赋值问题。</strong></p>
<h1 id="详细代码执行流程"><a href="#详细代码执行流程" class="headerlink" title="详细代码执行流程"></a>详细代码执行流程</h1><h2 id="1-首先React先挂载Calculator组件。而Calculator组件会调用render-渲染页面UI"><a href="#1-首先React先挂载Calculator组件。而Calculator组件会调用render-渲染页面UI" class="headerlink" title="1.首先React先挂载Calculator组件。而Calculator组件会调用render()渲染页面UI"></a>1.首先React先挂载<code>Calculator</code>组件。而<code>Calculator</code>组件会调用<code>render()</code>渲染页面UI</h2><h2 id="2-Calculator组件的render-内定义一些变量接收数据。其中用到了三元表达式来调用温度单位换算或者赋值"><a href="#2-Calculator组件的render-内定义一些变量接收数据。其中用到了三元表达式来调用温度单位换算或者赋值" class="headerlink" title="2. Calculator组件的render()内定义一些变量接收数据。其中用到了三元表达式来调用温度单位换算或者赋值"></a>2. <code>Calculator</code>组件的<code>render()</code>内定义一些变量接收数据。其中用到了三元表达式来调用温度单位换算或者赋值</h2><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">// 页面初始值</span><br><span class="line">const scale = this.state.scale;</span><br><span class="line">const temperature = this.state.temperature;</span><br><span class="line">// 如果是f，就调用tryConvert()进行温度换算，否则赋值temperature给scale</span><br><span class="line">const celsius =</span><br><span class="line">  scale === &quot;f&quot; ? tryConvert(temperature, toCelsius) : temperature;</span><br><span class="line">const fahrenheit =</span><br><span class="line">  scale === &quot;c&quot; ? tryConvert(temperature, toFahrenheit) : temperature;</span><br></pre></td></tr></table></figure>

<h2 id="3-在Calculator组件的render-内的return-有三个组件。"><a href="#3-在Calculator组件的render-内的return-有三个组件。" class="headerlink" title="3.在Calculator组件的render()内的return()有三个组件。"></a>3.在<code>Calculator</code>组件的<code>render()</code>内的<strong><code>return()</code></strong>有三个组件。</h2><h3 id="A-两个输入框组件：TemperatureInput"><a href="#A-两个输入框组件：TemperatureInput" class="headerlink" title="A. 两个输入框组件：TemperatureInput"></a>A. 两个输入框组件：<code>TemperatureInput</code></h3><h4 id="1-TemperatureInput输入框组件需要接收3个参数：scale温度符号、temperature温度数值、onTemperatureChange调用哪个温度单位转换函数"><a href="#1-TemperatureInput输入框组件需要接收3个参数：scale温度符号、temperature温度数值、onTemperatureChange调用哪个温度单位转换函数" class="headerlink" title="1. TemperatureInput输入框组件需要接收3个参数：scale温度符号、temperature温度数值、onTemperatureChange调用哪个温度单位转换函数"></a>1. <code>TemperatureInput</code>输入框组件需要接收3个参数：<code>scale</code>温度符号、<code>temperature</code>温度数值、<code>onTemperatureChange</code>调用哪个温度单位转换函数</h4><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line">return (</span><br><span class="line">    &lt;div&gt;</span><br><span class="line">        &#123;/* </span><br><span class="line">              传入摄氏度</span><br><span class="line">              传入摄氏度函数</span><br><span class="line">         */&#125;</span><br><span class="line">        &lt;TemperatureInput</span><br><span class="line">            scale=&quot;c&quot;</span><br><span class="line">            temperature=&#123;celsius&#125;</span><br><span class="line">            onTemperatureChange=&#123;this.handleCelsiusChange&#125;</span><br><span class="line">        /&gt;</span><br><span class="line">        &lt;TemperatureInput</span><br><span class="line">            scale=&quot;f&quot;</span><br><span class="line">            temperature=&#123;fahrenheit&#125;</span><br><span class="line">            onTemperatureChange=&#123;this.handleFahrenheitChange&#125;</span><br><span class="line">         /&gt;</span><br><span class="line">        &lt;BoilingVerdict celsius=&#123;parseFloat(celsius)&#125; /&gt;</span><br><span class="line">    &lt;/div&gt;</span><br><span class="line">);</span><br></pre></td></tr></table></figure>

<h4 id="2-在render-内接受父组件Calculator的值，例如温度temperature，以及onChange事件执行函数"><a href="#2-在render-内接受父组件Calculator的值，例如温度temperature，以及onChange事件执行函数" class="headerlink" title="2. 在render()内接受父组件Calculator的值，例如温度temperature，以及onChange事件执行函数"></a>2. 在<code>render()</code>内接受父组件<code>Calculator</code>的值，例如温度<code>temperature</code>，以及<code>onChange</code>事件执行函数</h4><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line">render() &#123;</span><br><span class="line">  // 接收父组件传递来的温度数值</span><br><span class="line">  const temperature = this.props.temperature;</span><br><span class="line">  // 接收温度标识符。如c或者f。C是摄氏度，F是华氏度</span><br><span class="line">  const scale = this.props.scale;</span><br><span class="line">  // 输入框，带有onChange处理函数</span><br><span class="line">  return (</span><br><span class="line">    &lt;fieldset&gt;</span><br><span class="line">      &lt;legend&gt;请输入温度 / &#123;scaleNames[scale]&#125;&lt;/legend&gt;</span><br><span class="line">      &lt;input value=&#123;temperature&#125; onChange=&#123;this.handleChange&#125; /&gt;</span><br><span class="line">    &lt;/fieldset&gt;</span><br><span class="line">  );</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h4 id="3-该组件的render-会渲染出一个输入框"><a href="#3-该组件的render-会渲染出一个输入框" class="headerlink" title="3. 该组件的render()会渲染出一个输入框"></a>3. 该组件的<code>render()</code>会渲染出一个输入框</h4><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line">render() &#123;</span><br><span class="line">    // 接收传递来的温度数值</span><br><span class="line">    const temperature = this.props.temperature;</span><br><span class="line">    // 接收温度标识符。如c或者f。C是摄氏度，F是华氏度</span><br><span class="line">    const scale = this.props.scale;</span><br><span class="line">    // 输入框，带有onChange处理函数</span><br><span class="line">    return (</span><br><span class="line">        &lt;fieldset&gt;</span><br><span class="line">            // scaleNames[]数组里是存放华氏度和摄氏度的全称，如 c: &quot;Celsius&quot;</span><br><span class="line">            &lt;legend&gt;请输入温度 / &#123;scaleNames[scale]&#125;&lt;/legend&gt;</span><br><span class="line">            &lt;input value=&#123;temperature&#125; onChange=&#123;this.handleChange&#125; /&gt;</span><br><span class="line">        &lt;/fieldset&gt;</span><br><span class="line">    );</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h4 id="4-上面的input框有一个onChange事件，调用了handleChange-方法，代码如下："><a href="#4-上面的input框有一个onChange事件，调用了handleChange-方法，代码如下：" class="headerlink" title="4. 上面的input框有一个onChange事件，调用了handleChange()方法，代码如下："></a>4. 上面的input框有一个<code>onChange</code>事件，调用了<code>handleChange()</code>方法，代码如下：</h4><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">handleChange(e) &#123;</span><br><span class="line">    // 调用父组件的handleCelsiusChange方法。而handleCelsiusChange方法是由父组件内的this.handleCelsiusChange提供的。</span><br><span class="line">    // 而this.handleCelsiusChange是保存数据的作用，最终该数据会被tryConvert()方法调用，来做温度单位转换</span><br><span class="line">    // 这行代码是调用父组件的onTemperatureChange()方法，然后传入当前输入框的value值，也就是用户输入的数字</span><br><span class="line">    this.props.onTemperatureChange(e.target.value);</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>在input输入框里输入数字的时候，会实时把value传入到 <code>this.props.onTemperatureChange(e.target.value)</code>并调用。而<code>onTemperatureChange()</code>实际上在调用<code>handleCelsiusChange()</code>来保存用户输入的数据到state内。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">// 保存 摄氏度 数据</span><br><span class="line">handleCelsiusChange(temperature) &#123;</span><br><span class="line">  this.setState(&#123; scale: &quot;c&quot;, temperature &#125;);</span><br><span class="line">&#125;</span><br><span class="line">// 保存 华氏度 数据</span><br><span class="line">handleFahrenheitChange(temperature) &#123;</span><br><span class="line">  this.setState(&#123; scale: &quot;f&quot;, temperature &#125;);</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>例如在<code>handleCelsiusChange(temperature)</code>的<code>temperature</code>就是</p>
<h3 id="B-一个提供沸腾信息显示的BoilingVerdict，判断celsius是否大于等于100"><a href="#B-一个提供沸腾信息显示的BoilingVerdict，判断celsius是否大于等于100" class="headerlink" title="B. 一个提供沸腾信息显示的BoilingVerdict，判断celsius是否大于等于100"></a>B. 一个提供沸腾信息显示的<code>BoilingVerdict</code>，判断<code>celsius</code>是否大于等于100</h3><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">// 是否是开水</span><br><span class="line">function BoilingVerdict(props) &#123;</span><br><span class="line">    if (props.celsius &gt;= 100) &#123;</span><br><span class="line">        return &lt;p&gt;水开了&lt;/p&gt;;</span><br><span class="line">    &#125;</span><br><span class="line">    return &lt;p&gt;水还没有沸腾&lt;/p&gt;;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h1 id="总结"><a href="#总结" class="headerlink" title="总结"></a>总结</h1><ol>
<li><p>React挂载组件<code>&lt;Calculator /&gt;</code></p>
</li>
<li><p><code>&lt;Calculator /&gt;</code>里，定义了初始值温度、温度单位、温度转换函数，以及渲染了2个输入框，1个文本提示。初始值均为空字符串</p>
</li>
<li><p>给输入框组件<code>&lt;TemperatureInput /&gt;</code>传递了三个参数：<em>scale</em>、<em>temperature</em>、<em>onTemperatureChange</em>。这三个参数初始值默认为空</p>
<p><em>scale</em>：    温度的单位；初始值为空，后续根据用户在哪个输入框里输入，来赋值。</p>
<p><em>temperature</em>：    已经计算好温度；初始值空字符串，后续根据用户的输入框来赋值。</p>
<p><em>onTemperatureChange</em>：    调用父组件的<code>handleCelsiusChange</code>方法。而<code>handleCelsiusChange</code>方法是由父组件内的<code>this.handleCelsiusChange</code>提供的。而<code>this.handleCelsiusChange</code>是保存数据的作用，最终该数据会被<code>tryConvert()</code>方法调用，用来做温度单位转换。<strong>其中这个参数重中之重，因为该参数准确的作用是将父组件的方法传递给子组件调用，从而实现了子组件向父组件赋值的功能，也就是所谓的状态提升</strong></p>
</li>
</ol>
<h1 id="完整代码"><a href="#完整代码" class="headerlink" title="完整代码"></a>完整代码</h1><p>完整注释：<a href="https://gist.github.com/shanlanCoding/725bc0b068f359e29f6e1bf31a1019cc" target="_blank" rel="noopener">https://gist.github.com/shanlanCoding/725bc0b068f359e29f6e1bf31a1019cc</a></p>
<p>在线演示： <a href="https://codepen.io/gaearon/pen/WZpxpz" target="_blank" rel="noopener">https://codepen.io/gaearon/pen/WZpxpz</a></p>
<h1 id="效果图"><a href="#效果图" class="headerlink" title="效果图"></a>效果图</h1><p><img src="https://zh-hans.reactjs.org/react-devtools-state-ef94afc3447d75cdc245c77efb0d63be.gif" alt="效果图"></p>

      
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